The present invention is concerned with a titanium dioxide suspension with a high solids content and a process for the preparation thereof. More specifically, the present invention relates to a finely divided dryly precipitated titanium dioxide which is first converted into an aqueous slurry containing precipitated titanium dioxide in unflocculated condition; the slurry is then dechlorinated and filtered, and the resultant filter cake is rendered flowable with the aid of a dispersing agent. The product is especially useful in paper manufacture where titanium dioxide suspension is particularly useful as a raw material to meet the requirements of manufacturers for a liquid system to be used at their plant facilities.
The preparation of finely divided titanium dioxide through reaction of titanium tetrachloride in the vapor phase with an oxygen-containing gas, the so-called "chloride titanium dioxide process", has become increasingly important in producing titanim dioxide for world markets. There today exists the requirement to transport large quantities of titanium dioxide in the form of a highly stable aqueous suspension.
In a representative prior art process for preparation of a titanium dioxide suspension, as described for example in U.S. Pat. No. 3,536,510, a dry, ground post-treated titanium dioxide pigment is dispersed in water with the use of a dispersing agent. In other prior art processes, the solids content of the dispersion is increased through various processes of reducing the water content ("dewatering"). For example as described in U.S. Pat. No. 3,758,322 a flocculating agent is added to an approximately 20% (weight) titanium dioxide pigment slurry, the flocculated slurry is filtered, and a filter cake with a titanium dioxide solids content of 60 to 80% (weight) is obtained. This filter cake is again rendered flowable via stirring and the addition of a dispersing agent. Before being rendered flowable, however, the filter cake must be freed of the flocculating agent through expensive washing steps.
In U.S. Pat. No. 4,280,849, an expensive and complicated two-stage filtration process is described. U.S. Pat. No. 4,978,396 describes a process in which a titanium dioxide slurry prepared in an unflocculated condition with the aid of a first dispersing agent is dewatered via pressure filtration. The filter cake is made then flowable by the addition of a second dispersing agent. Because of the first dispersing agent, there is significant filtration loss in the filtration. A considerably cloudy filtrate is obtained which requires complicated and costly processing.